Field of the Invention
The present invention relates to a printing element substrate including a printing element which forms information such as a character or figure on a printing medium such as paper or cloth, a printhead including the printing element substrate, and a printhead manufacturing method.
Description of the Related Art
To meet a demand for a higher printing speed in inkjet printers, there has been proposed a line head configured by arranging a plurality of printing element substrates in a predetermined direction at the same width as the width (to be referred to as printing width) of a printing medium. This printhead is fixed and can print simultaneously at the printing width, achieving higher-speed printing than by a serial printer which prints by reciprocating the printhead. Japanese Patent Laid-Open No. 2007-296638 (to be referred to as a literature) discloses an example of the structure of the line head.
FIG. 1 in the literature shows the outer appearance of a printhead after assembly. FIG. 3 in the literature is an exploded view of the printhead shown in FIG. 1.
Referring to FIGS. 1 and 3 in the literature, a plurality of printing element substrates H1100a to H1100d are arranged in a predetermined direction on a first plate H1200, and electrically connected to an electrical wiring board H1300 by wire bonding or the like. A printer main body supplies power and control signals to the printing element substrates H1100 via an external signal input terminal H1301 arranged on the electrical wiring board H1300.
FIG. 9 in the literature shows signal wiring between the four printing element substrates H1100a to H1100d. Signals HEAT1 to HEAT8 and IDATA1 to IDATA8 are individually supplied from the respective printing element substrates to external signal input terminals. HEAT1 to HEAT8 are pulse signals to be supplied to printing elements on the respective printing element substrates. IDATA1 to IDATA8 are data signals for selecting desired printing elements on the respective printing element substrates in synchronism with DCLK. FIG. 10 in the literature shows the timings of respective signals.
The line head type printhead can print on a wider printing medium by increasing the number of printing element substrates arranged along the printing width. However, as the number of printing element substrates increases, the number of input terminals of the line head also increases. Also when implementing higher-resolution printing of photographic quality by the line head, it is effective to increase the printing element density with respect to the printing width on the printing element substrate or increase the number of printing element arrays along the printing width. In this case, the number of printing elements per printing element substrate increases. A larger number of printing elements leads to a larger number of data to be input to the printing element substrate. To cope with a larger number of data without decreasing the printing speed, the data transfer speed needs to be increased. When the wiring from the head input terminal to the printing element substrate becomes long, like the line head, the waveform may deteriorate midway along the wiring or data may be garbled by external noise entering the wiring. This makes high-speed data transfer difficult.
To solve this problem, a low voltage differential signaling (LVDS) scheme is effective. FIG. 14 is a circuit diagram exemplifying the transmitting and receiving sides according to the related LVDS scheme.
As shown in FIG. 14, in LVDS data transfer, a transmitter 1401 on the transmitting side outputs a signal as a current, and a receiver 1402 on the receiving side converts the input current into a voltage. To transfer data quickly without distorting the data transfer waveform, impedances on the transmitting and receiving sides desirably match each other, and the receiving end requires a terminating resistance element.
When impedances on the data transmission line and the terminating resistance element at the receiving end match each other, the data transfer waveform becomes a waveform as shown in FIG. 15A. If impedances on the line and terminating resistance element do not match each other, the data transfer waveform distorts owing to reflection, as shown in FIG. 15B, inhibiting high-speed data transfer. To avoid the impedance mismatch, an external resistive element having a guaranteed resistance is effectively mounted near the receiving end.
However, it is difficult to mount a component such as the resistive element near the end of the printing element substrate of the printhead in terms of reliability and maintenance due to requests for insulation of the resistive element from ink and flatness of the head surface when wiping ink from the head surface. As the terminating resistance element, a printing element formed on a printing element substrate by a semiconductor process may be used. Such a printing element substrate is manufactured using a semiconductor manufacturing process, and many printing element substrates are fabricated at once from one silicon wafer. Printing element substrates obtained by the semiconductor manufacturing process vary in the resistance of the resistive element by 20 to 30% under the influence of manufacturing variations. Therefore, even if the resistive element is arranged, some printing element substrates may generate an impedance mismatch to distort the data transfer waveform, failing high-speed data transfer again.
To reduce such manufacturing variations, there is known a method of trimming a resistive element by a laser or the like to adjust the resistance to a predetermined value. However, this method raises the manufacturing cost. In addition, if the laser damages the substrate surface, insulation of the resistive element from ink may be impaired, resulting in poor reliability.